Field
Embodiments of the invention relate to a polishing composition used for polishing electronic components, such as semiconductors and magnetic recording media including hard disks. Particularly, embodiments of the invention relate to a polishing composition used for surface polishing of a substrate for a magnetic recording medium, such as a glass magnetic disk substrate and an aluminum magnetic disk substrate. Further, embodiments of the invention relate to a polishing composition used for surface polishing of an aluminum magnetic disk substrate for a magnetic recording medium, wherein the substrate has a coating formed by electroless nickel-phosphorus plating on the surface of a substrate of an aluminum alloy.
Description of the Related Art
In the past, use has been made of polishing compositions in which alumina particles with relatively large particle sizes which can provide a high polishing rate are dispersed in water from the viewpoint of productivity, as a polishing composition for polishing a surface coated by electroless nickel-phosphorus plating, of an aluminum magnetic disk substrate. However, the use of alumina particles has caused a problem that since alumina particles are considerably harder than a coating deposited by electroless nickel-phosphorus plating on an aluminum magnetic disk substrate, alumina particles are embedded in the substrate and the embedded particles have an adverse effect on the subsequent polishing step.
As solutions to this problem, polishing compositions have been proposed in which alumina particles and silica particles are combined. There have also been proposed methods in which polishing is performed, with no use of alumina particles, using only silica particles.
According to the conventional art, it is possible that by combining alumina particles and silica particles, the alumina particles that are embedded in the substrate are removed to some degree. However, as long as a polishing composition including alumina particles is used, there still remains the possibility that the alumina particles contained in the polishing composition are embedded in the substrate. In addition, since the proposed polishing compositions include both alumina particles and silica particles, there is caused a problem that the respective properties possessed by the alumina particles and by the silica particles are negated with each other, leading to worsening of the polishing rate and surface smoothness.
For these reasons, there have been proposed methods in which polishing is performed, with no use of alumina particles, using only silica particles. According to the conventional art, it is proposed to combine colloidal silica and a polishing accelerator. According to other conventional art, methods are proposed in which polishing is performed using colloidal silica, as well as fumed silica, surface modified silica, silica produced in water glass process, and other types of silica, in particular colloidal silica having particular shapes. However, these methods do not achieve a sufficient polishing rate, and are required to make improvements. According to other conventional art, a method is proposed in which colloidal silica and fumed silica are used in combination. However, while this method results in an improvement in the polishing rate, the fumed silica has very low bulk density, leading to significant worsening of workability, such as in the preparation of slurries, and also having concerns about health due to its dusts. According to other conventional art, a method is proposed in which crushed silica particles are used, thereby to obtain a polishing rate approximate to that obtained when alumina particles are used. However, this method has a problem of worsening the surface smoothness, and is required to make improvements.